Implant Tribune United Kingdom Edition

January 201414 Implant Tribune United Kingdom Edition the load energy** which led to reduction of stress concentration and rate of stress deterioration by moving away from implants. That is considered better distribution of stresses from the mechanics point of view, which may result in longer lifetime. Porcelain coating showed less stress in case of two implants, longer life for the brittle coating material is expected. Contrarily more stresses were found on the gold crown placed on two implants due to its volume reduction (less material under the same load). This is clearly seen in increasing stresses on the two implants, that more load effect was transferred through the weak crown to the two im- plants. That showed maximum stresses in the area under the crown, while the wide implant showed maximum stresses at its tip. Looking to energy** absorp- tion and stress concentration on whole system starting from coat- ing to cortical and spongy bone, although the stress levels found was too low and far from crack- ing danger, the following conclu- sions can be pointed out; the total results favour the two implants in spongy bone and the wide im- plant in the cortical layer, but the alveolar bone consists of spongy bone surrounded by a layer of cortical bone. It’s also well known that according to the degree of bone density the alveolar bone is classified to D1,2,3,4 23 in a de- scending order. So, provided that the edentu- lous space after the molar extrac- tion permits, it’s recommended in the harder bone quality (D1,2) to use one wide diameter implant and in the softer bone (D3,4) quality two average sized im- plants. Therefore more detailed study to compromise between the two implants size/design and intermediate space can put this stress values in safe, acceptable, and controllable region under higher levels of loading. **The area under the __-__ curve up to a given value of strain is the total mechanical energy per unit volume consumed by the material in straining it to that value (Fig. 9). This is easily shown as follows in equation 2 : Summary Restoration of single molar using implants encounters many prob- lems; mesio-distal cantilever due to very wide occlusal table is the most prominent. An increased occlusal force posteriorly wors- ens the problem and increases failures. To overcome the over- load, the use of wide diameter implants or two regular sized im- plants were suggested. The aim of this study was to verify the best solution that has the best effect on alveolar bone under distrib- uted vertical loading. Therefore, a virtual experiment using Finite Element Analysis was done us- ing ANSYS version 9. A simplified simulation of spongy and cortical bones of the jaw as two co-axial cylinders was utilised. Full de- tailed with high accuracy simu- lation for implant, crown, and coating was implemented. The comparison included different types of stresses and deforma- tions of both wide implant and two regular implants under the same boundary conditions and load application. The three main stresses com- pressive, tensile, shear and the equivalent stresses in addition to the vertical deformity and the total deformities were consid- ered in the comparison between the two models. The results were obtained as percentages using the wide implant as a reference. The spongy bone showed about five per cent less stresses in the two implants model than the one wide diameter implant. The exceptions are the relatively in- crease in maximum compressive stresses and deformations of or- der 12 per cent and 0.3 per cent respectively. The stresses and displace- ments on the cortical bone are higher in the two implant model due to having two close holes, which results in weak area in-be- tween. The spongy bone response to the two implants was found to be better considering the stress distribution (energy absorbed by spongy bone**). Therefore, it was concluded that, using the wide diameter implant or two average ones as a solution depends on the case primarily. Provided that the available bone width is suf- ficient mesio distally and bucco- lingualy, the choice will depend on the type of bone. The harder D1,2 types having harder bone quality and thicker cortical plates are more convenient to the wide implant choice. The D3,4 types consist of more spongy and less cortical bone, are more suitable to the two implant solution. DT Editorial note: A complete list of references is available from the author. About the author Prof. Amr Abdel Azim Professor, Faculty of Dentistry, Cairo University drazim@link.net Dr Amani M. Zaki GBOI. 2009, Egypt amani.m.zaki@gmail.com Dr Mohamed I. El-Anwar Researcher, Mechanical Engineering Department, National Research Center, Egypt anwar_eg@yahoo.com page 13DTß Fig 6b Fig 7a Fig 7b Fig 8a Fig 8b Fig 9 Fig 10 Table 1 Table 2 page 13DTß classified to D1,2,3,423 in a de-

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